arrays - PHP json object has duplicate values with numeric and associative keys -

my php function returns following json object:

{"user_id":"1",   "0":"1",    "token":null,   "1":null,    "username":"bgarrett0",   "2":"bgarrett0"} 

it adding both numeric key/values , associative key/values. want associative/values. $sql prepared query string, args array of appropriate values $sql.

$this->pdo (mysql db) has attributes [pdo::attr_errmode, pdo::errmode_exception;pdo::attr_emulate_prepares, false;]

   public function query($sql, $args)    {     try {         $stmt = $this->pdo->prepare($sql);         $stmt->execute($args);         $stmt = $stmt->fetchall();         return json_encode($stmt);     } catch(exception $e) {         $this -> error_status = $e->getmessage();     }   } 

then use flag pdo::fetch_assoc if want associative indices:

$data = $stmt->fetchall(pdo::fetch_assoc); return json_encode($data);